RON12, a novel Plasmodium-specific rhoptry neck protein important for parasite proliferation

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Abstract

Apicomplexan parasites invade host cells by a conserved mechanism: parasite proteins are secreted from apical organelles, anchored in the host cell plasma membrane, and then interact with integral membrane proteins on the zoite surface to form the moving junction (MJ). The junction moves from the anterior to the posterior of the parasite resulting in parasite internalisation into the host cell within a parasitophorous vacuole (PV). Conserved as well as coccidia-unique rhoptry neck proteins (RONs) have been described some of which associate with the MJ. Here we report a novel RON, which we call RON12. RON12 is found only in Plasmodium and is highly conserved across the genus. RON12 lacks membrane anchors and is a major soluble component of the nascent PV. The bulk of the secretion of RON12 happens late during invasion (after parasite internalisation) allowing accumulation in the fully formed PV with a small proportion of RON12 also apparent in structures resembling the MJ. RON12, unlike most other RONs is not essential, but deletion of the gene does affect parasite proliferation. The data suggest that although the overall mechanism of invasion by Apicomplexan parasites is conserved, additional components depending on the parasite - host cell combination are required.